This invention relates to ground fault detectors for electrical distribution systems, and more particularly to ground fault detectors which respond to a wide range of ground fault current levels from ungrounded electrical distribution systems.
Paragraph 503-13 of the National Electrical Code 1975 requires a ground fault detector or indicator which provides an audio and visual alarm whenever a ground fault from an ungrounded electrical power distribution system occurs and persists. Ungrounded distribution systems are preferred and frequently used in the textile industry and in other production-line industries since a ground fault is not fatal to the operation of an ungrounded distribution system as long as two or more ground faults are not simultaneously present. Also, repair of any component or device in the power system can be effected without shutting down the distribution system and consequently the production line.
The problem with designing ground fault detectors for textile mills or production lines is that a wide variety of equipment and electrical distribution apparatus is encountered and varying degrees of ground fault protection are desirable. Accordingly, a major object of this invention is to provide a single ground fault detector which is responsive to a wide range of ground fault current levels.
Another problem of providing ground fault protection for industrial environments is to prevent or minimize false ground fault detection due to the presence of high electrical noise levels. To this end, another object of the invention is to provide varying degrees of filtering of potential ground fault signals to prevent the generation of false ground fault alarms due to electrical noise.
Other objects and advantages of the invention will become apparent as the description of the invention proceeds.